Patent GB-1204660-A (GB)
Title: Hydraulic control rod drive system
IPC: G21C7/16
Filed: 1969-06-26
Abstract: 1,204,660. Controlling reactors. UNITED STATES ATOMIC ENERGY COMMISSION. 26 June, 1969 [24 July, 1968], No. 32280/69. Heading G6C. An hydraulically actuated control rod drive system comprises a control rod guide tube 13<SP>1</SP> vertically positioned in a sodium-cooled fast reactor core 15 and loosely housing a control rod 14<SP>1</SP>, there being an aperture 19 in the upper end of the guide tube 13<SP>1</SP> while its lower end is connected via a tap line 25 with a main line 26. The guide tube 13<SP>1</SP> forms part of a fuel bundle (not shown) in which a number of fuel rods together with the guide tube are housed within a hexagonal casing, a plurality of these fuel bundles forming the reactor core 15. The core 15 is mounted within a pressure vessel 16 and surrounded by liquid sodium coolant. Main line 26 extends through the wall of the reactor vessel 16 and is coupled at 28 with a pair of lines 29, 30. An " up " valve 34 and a " scram " valve 35 are mounted in line 30 and a " down " valve 31 in line 29, lines 29, 30 being coupled at 36 to a line 37 connected to a low pressure tank 22. A pressure supply line 41 connects a sodium pump 20 with line 30 at 42. A feed valve 43 and a restrictive orifice 44 are mounted in supply line 41. In order to raise control rod 14<SP>1</SP> from the position shown, the " up " valve 34 is opened allowing fluid flow from sodium pump 20 via lines 41, 30, 26, 25 to the lower end of guide tube 13<SP>1</SP>. The restrictive orifice 44 is sized to provide only sufficient flow to raise the control rod 14<SP>1</SP> (or associated group of control rods) and provide for the leakage between rod 141 and guide tube 131 due to the loose fit of the rod, which leakage is discharged via the aperture 19. A differential pressure gauge 48 in parallel with the orifice 44 shows a pressure drop during transit of the rod 14<SP>1</SP>, but when the rod is firmly seated on the face seal 17 at the upper end of the guide tube 13<SP>1</SP>, the gauge 48 shows a near-zero reading. A second control rod (or group of control rods) can then be raised in like manner. If the fluid supply should fail, the rods 14<SP>1</SP> will all fall into the core 15 and a subsequent restarting of the pump 20 cannot lift any of the rods unless only a single " up " valve 34 is open. Normal lowering of the rods 14<SP>1</SP> is accomplished by closing valve 34 and allowing the rods to descend by gravity. Emergency reactor shut-down is accomplished by opening " scram " valve 35, valve 34 being open, which suddenly lowers the pressure below all the control rods which are in the up position by connecting line 26 via lines 30 and 37 with low pressure tank 22. In order to indicate a down position of a group of control rods 14<SP>1</SP>, a sampling method is used. Opening " down " valve 31, with " up " valve 34 closed, exposes the lower ends of the rods 14<SP>1</SP> through lines 25, 26, 29, 37 and a restrictive orifice 33 to the low pressure tank 22. If all the rods are seated in the down position on face seals 18, pressure gauge 32 in line 29 will show a low pressure reading. However, if one or more of the rods are not so seated the gauge 32 will show a higher reading and orifice by-pass valve 40 is then opened, greatly reducing the pressure below the control rod(s) and forcing the rod(s) down by coolant pressure via aperture(s) 19. To modify the above-described hydraulic control rod drive system for use in a boiling water reactor, the sodium pump 20 is replaced by a feedwater pump and the low pressure tank 22 is connected to a condenser instead of to a vacuum pump 24.